1. Field of the Invention
The present invention relates to a substrate for ink ejection heads, an ink ejection head, a method of manufacturing the substrate, and a method of manufacturing the ink ejection head.
2. Description of the Related Art
Liquid ejection recording methods are those of performing recording in such a manner that liquids such as ink are ejected through discharge ports arranged in liquid ejection heads so as to be applied to recording media such as sheets of paper. A liquid ejection recording method in which a liquid is ejected in such a manner that the liquid is bubbled by thermal energy generated by an energy-generating element is capable of forming a high-quality image and capable of performing high-speed recording.
In general, a liquid ejection head includes a plurality of discharge ports, a passage communicatively connected to the discharge ports, and a plurality of energy-generating elements generating thermal energy used to eject ink. The energy-generating elements include heat-generating resistor layers. The heat-generating resistive layers are covered with an upper protective layer for protecting the energy-generating elements from liquids and include lower layers for storing heat.
In methods of manufacturing conventional liquid ejection heads, the distance between each heat-generating resistive element and a corresponding one of discharge ports is set with high accuracy and reproducibility such that high-quality recording can be performed.
U.S. Pat. No. 5,478,606 discloses a method of manufacturing a liquid ejection head. The method includes forming a passage pattern using a soluble resin, coating a solid with a coating resin such as an epoxy resin at room temperature, forming discharge ports, and dissolving the soluble resin.
The following method is known: a method in which a coating resin for forming a passage member is attached to a substrate in such a manner that an adhesive layer made of a polyether amide resin is placed therebetween. The substrate carries energy-generating elements used to eject ink, an insulating layer overlying the energy-generating elements, and the like. FIG. 11 is a perspective view of a liquid ejection head disclosed in U.S. Pat. No. 6,390,606. FIG. 12 is a sectional view of the liquid ejection head taken along the line XII-XII of FIG. 11. The liquid ejection head includes a substrate; an electrode interconnect 221 formed by gold plating; and, for example, a titanium-tungsten layer 220 for preventing gold from diffusing into the substrate. The titanium-tungsten layer 220 is disposed under the electrode interconnect 221 and contains a refractory metal.
The substrate is disposed under the titanium-tungsten layer 220 and includes a P—SiN layer 219, electrode layer 218, and interlayer insulating layer 217 arranged in that order. The P—SiN layer 219 is located at the top of the substrate.
The electrode interconnect 221 is overlaid with a metal layer 222 having high adhesion with an organic resin for ejecting ink.
The development of elongated substrates requires the use of electrode interconnects made of gold, which has low resistance, and causes an increase in the contact area between an electrode interconnect and a P—SiN layer located at the top of each of the elongated substrates.
In order to increase the heat efficiency of heat-generating resistors for energy saving, it is highly predictable that a P—SiN layer located at the top of each substrate needs to have a reduced thickness.
In the case of reducing the resistance of electrode interconnects for supplying electric power to heat-generating resistors in a method of manufacturing the liquid ejection head disclosed in U.S. Pat. No. 6,390,606, the electrode interconnects are preferably formed by a plating process using gold, which is a good material with low resistance. In particular, an electrode layer made of gold is preferably provided above the substrate used in the liquid ejection head.
In the case of forming electrode interconnects by a conventional electroplating process, there is a problem below.
In the conventional electroplating process, after a diffusion-preventing layer made of a refractory metal and a gold seed layer are formed over a wafer, resist patterning is performed and a gold plating layer is then formed; hence, the diffusion-preventing layer is sandwiched between the gold plating layer and the wafer.
When a substrate obtained from the wafer has surface defects such as pinholes, the substrate is probably shorted with electrode interconnects prepared from the gold plating layer.
This is probably because the elongation of the substrate leads to an increase in the length and area of each gold electrode interconnect to cause short-circuits between the substrate and the electrode interconnects.
In this case, a thick P—SiN layer is provided on the substrate so as to cover defects such as pinholes or an insulating layer is added. However, this probably causes a reduction in energy efficiency or productivity.